<!DOCTYPE html>
<!-- 改变索引值为等于 3 的 div 元素的背景色为 # bbffaa -->
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript">
	$(document).ready(function() {
		$("div:eq(3)").css("background-color", "#bbffaa");
	});
</script>
</head>
<body>
    <div>1</div>
	<div>1</div>
	<div>1</div>
	<div>1</div>
	<div>1</div>
	<div>1</div>
	<div>1</div>
	<div>1</div>
</body>
</html>